1. Field of the Invention
The invention relates to crosslinkable compositions based on organosilicon compounds with very good handling properties during use, to processes for preparation thereof, and also to the use thereof.
2. Description of the Related Art
Single-component sealing compositions which can be stored if water is excluded but which on ingress of water vulcanize at room temperature to give elastomers are known. Large amounts of these products are used, for example, in the construction industry. These mixtures are based on polymers which have terminal silyl groups bearing reactive substituents such as OH groups or hydrolyzable groups, e.g. alkoxy groups or acetoxy groups. These sealing compositions can moreover comprise fillers, plasticizers, crosslinking agents, catalysts, and also additives. Additives in sealing compositions not only optimize selected aspects of performance of the cured product, but can also improve the specific properties of the sealing composition during the curing process and indeed during the application process.
The sealing compositions are usually expressed from tubes, cartridges or tubular bags, and then smoothed within a joint with the finger or with a smoothing aid. They remain in the joint without substantially changing shape until complete curing has occurred. Rheology additives which have an effect on the physical stability of uncured sealing compositions are described, for example, in U.S. Pat. No. 4,304,897. The polyether silicone copolymers described therein reduce the flow properties of silicone sealing compositions, the result being that they have no or only minimal flow under the influence of gravity, i.e. under the influence of very small shear forces.
The paste-like sealing composition must meet stringent requirements during the application process. For example, when the sealing composition is smoothed by the finger or by a smoothing tool it is desirable to provide maximum resistance, in order that the jointing process can be optimized. This resistance can be measured by technical methods, by measuring the force needed by a prescribed shaped object to achieve a certain depth of penetration. Another technical term used for resistance during smoothing is “body”. Users of sealing compositions often complain of insufficient “body”. Once the smoothing process has ended, it is desired that the sealing composition releases from the smoothing tool without extended stringing, thus permitting clean finishing of the joint.
EP-A 857 760 describes a wide variety of non-ionic compounds for reducing the level of stringing of silicone sealing compositions, inter alia polyethylene-polypropylene block copolymers. The property known as “body”, i.e. the resistance of the sealing composition during the jointing process described above, is not improved thereby, or at least not substantially so. To achieve sufficient resistance to deformation of the sealing composition, the known nonionic compounds would also have to be present in amounts which markedly impair the adhesion of the sealing composition to substrates. Addition of these amounts is not possible, in practice.
Another known method for increasing resistance to deformation of the uncured sealing composition consists of increasing the proportion of fine-particle fillers which are generally always present. However, the amounts of fine-particle fillers that must be incorporated into the mixtures in order to achieve satisfactory application properties are such that the excessive filler content gives the subsequently cured rubber a level of mechanical properties that is inadequate for jointing applications, examples being excessive hardness or inadequate extensibility.
Achievement of ideal application properties in silicone sealing compositions is rendered yet more difficult overall by the presence, in accordance with the prior art, of non-silicone plasticizers in the sealing compositions. Organic hydrocarbons are generally used, these being obtained from work-up of the appropriate petroleum fractions during distillation. These greatly reduce the resistance which the sealing composition exerts on the tool during smoothing.